The Facts

Although it's considered a vaccine-preventable disease, whooping cough (pertussis) certainly hasn't been eliminated as a public health problem. The incidence of whooping cough has decreased by more than 90% over the last 50 years, but there are still outbreaks. While most other diseases that are vaccinated against in childhood are decreasing in frequency, cases of whooping cough have actually increased since 1990. This is likely due to the lower effectiveness of older vaccines (due to the emergence of new strains of the disease), decreased protection from the disease (immunity) in adults and adolescents as the effect of the vaccine wears off, and increased reporting of whooping cough by doctors.

About 2,000 to 10,000 cases a year have been reported in Canada over the last 10 years. In Canada, 1 to 3 Canadians die each year from whooping cough. In unvaccinated populations, most cases occur in children under 5, especially in babies less than 6 months old. Because the effects of the vaccination wear off, adults are also susceptible to the disease.

Causes

Whooping cough is caused by the bacterium Bordetella pertussis. The bacterium is transmitted in tiny droplets that come from the nose and mouth and is spread from person to person. A similar bacterium called Bordetella parapertussis causes a milder version of whooping cough known as parapertussis.

While most cases of pertussis occur in children under 5 years, it may be that the majority of carriers are older. It's now believed that adults are a major source of infection to infants.

Since many people reach adulthood without having been infected, it's entirely possible for adults to develop whooping cough. One Canadian study concluded that between 10% and 20% of coughs in adults and adolescents that last 7 days or more are caused by pertussis. After infants, the people most likely to suffer serious complications from whooping cough are seniors and those with chronic ill health.

The disease takes 1 or 2 weeks to incubate. People become infectious to others by the end of the first week and they typically remain contagious for about 6 weeks. The disease is highly contagious and you will be advised to avoid contact with others while you are still able to infect people.

Symptoms and Complications

The disease has 3 stages. The first stage begins about 10 days after infection and causes symptoms like a common cold - sneezing, watery eyes, tiredness, and loss of appetite. There's also a dry hacking cough.

The second stage occurs after 10 to 14 days and is signalled by a rapid increase in the frequency and severity of coughing. It's this cough that gives the disease its name. Half a dozen or more rapid coughs follow each other in quick succession, followed by a "whooping" sound as the person inhales deep and fast. It may happen hundreds of times in a single day. The coughing may produce large amounts of thick mucus. Sometimes infants swallow it, but it may exit through the nostrils, often forming bubbles. Frequent coughing and mucus can cause vomiting, and choking is a risk in infants. Infants are actually less likely to make the whooping sound than are older children or adults, but they're more likely to have a choking spell.

After a month, most people start to look and feel better and cough less. This is the third stage - a gradual recovery taking a few weeks or occasionally a few months. The usual total course of the disease lasts 6 to 10 weeks.

The risk of complications is highest in infants under one year old. There's also potential danger to seniors and those with chronic ill health. Complications include pneumonia, encephalitis (inflammation of the brain), seizures, apnea (brief periods when breathing stops), and hemorrhages (bleeding) in the eye.

Making the Diagnosis

Whooping cough is usually easy to diagnose. A cotton swab on the end of a wire is inserted through the nostril into the nasopharynx (the breathing tube behind the nose), and then cultured to look for bacteria. Most of the time, the bacteria will show up on this test. This means a few cases won't be diagnosable in the early stages, but once it gets to the second stage, the symptoms will make the nature of the condition obvious. In some cases, the disease runs a milder course and the later symptoms do not develop. People who have been immunized can still get whooping cough, but they will have much milder symptoms. Chest X-rays may also be taken to check for the presence of fluid or mucus in the lungs.

Treatment and Prevention

Although bacteria cause whooping cough, antibiotics aren't especially effective in treating it unless they're given in the first stage. Very often, the disease isn't recognized until it enters the second stage. Nevertheless, antibiotics such as erythromycin*, clarithromycin, azithromycin, or sulfamethoxazole - trimethoprim are given at this stage to reduce the possibility of complications, even if they don't cut the duration of the whooping cough itself.

Infants with pertussis are often hospitalized, especially those less than 6 months of age. Treatment is designed to minimize symptoms and the damage those symptoms can cause. In the case of heavy vomiting, fluids and electrolytes (e.g., potassium) must be replaced intravenously. In babies, it may be necessary to suck out mucus with a vacuum-like device or to install a nasal breathing tube to help breathing. Extra oxygen may also be necessary. Expectorant and cough-suppressing medications are generally not recommended. Babies with pertussis should be left to sleep as much as possible, since any disturbance or excitement is likely to trigger coughing. In older children, symptoms and risks are much milder, and hospitalization is hardly ever needed.

Most people know there's a vaccine against whooping cough; however, too many people know about it for the wrong reasons. Antivaccine groups and the media have focused on a one-in-a-million chance of encephalitis (severe brain inflammation) occurring in the hours or days after the vaccination, while not addressing the far larger risk of encephalitis caused by whooping cough in unvaccinated people.

The last sizeable Canadian outbreak of pertussis, in New Brunswick in 1998, was overwhelmingly concentrated in the 5 to 14 age group. This was a clear sign that vaccinations were allowed to lapse, because vaccinations given in infancy would have worn off by these ages.

The Canadian pertussis vaccination schedule is as follows: babies are given the DPT (diphtheria - pertussis - tetanus) vaccine at 2 months, 4 months, and 6 months of age to establish basic immunity. They are then given boosters at 18 months and at 4 to 6 years of age. The last booster should cover them to about age 14 to 16, when they are given the new whooping cough vaccine (see below) combined with the adult diphtheria - tetanus formulation. The first 5 shots (from 2 months to 4 to 6 years) will usually be given in conjunction with polio vaccine and Hemophilus influenzae B or "Hib" vaccine (an antipneumonia vaccine), since these have the same schedule as DPT. Additional immunizations are given with some of these first 5 shots, with the exact schedule determined by the province.

In the late 90's, a new pertussis vaccine that didn't contain whole killed Bordetella pertussis cells was introduced in Canada. The new vaccine is known as DTaP ("a" stands for acellular), while the old one is called DTwP ("w" is for whole). The new shot is even less likely to cause severe reactions than the old one. Because of recent evidence that many infants catch pertussis from adults, aP (acellular pertussis vaccine) is now available in a combined adult diphtheria - tetanus - acellular pertussis shot.

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.